This invention relates to steam generation control for a waste heat boiler, and in particular for steam control for a waste heat boiler in a Cheng dual fluid cycle (DFC) engine.
Waste heat boilers are used to recover unused or waste heat from engines, typically, gas turbine engines. This is done to increase the over-all system efficiency. More recently a waste heat boiler is used to recover waste heat in the Cheng DFC engine. This engine is described in U.S. Pat. No. 4,128,994 and in U.S. patent application Ser. No. 705,355 both entitled "Regenerative Parallel Compound Dual Fluid Heat Engine." There heat from waste gases is recovered by the waste heat boiler to convert water into superheated steam. The superheated steam, one of the two working fluids, is mixed with the other working fluid, typically gaseous combustion products. Work is provided by the combination of the two working fluids, in a manner which is greater than the sum of the two working fluids individually.
The typical waste heat boiler consists of an economizer, an evaporator, and a superheater. It also incorporates a recirculation pump between the output and input ends of the evaporator to recirculate the water at a much higher rate than it evaporates in the evaporator, guaranteeing good heat transfer.
The steam from the boiler has a control valve at the outlet from the superheater. It is logical and traditional that the steam control valve is located at the output end of the boiler. This control valve normally controls the rate of steam flow, for example, to a steam engine, a steam turbine, or a Cheng DFC engine.
Although this mode of steam control has existed for many years, disadvantages result from the location of the steam control valve at the output of the superheater. This is particularly the case where it is desired to maximize the temperature of the superheated steam, such as in the case of a Cheng DFC engine.